Research paperAnalysis on geologic conditions affecting the performance of gas production from hydrate deposits

- Gas production depends on permeability, porosity and initial hydrate saturation.
- Cumulative gas production is proportional to the permeability.
- Water-to-gas ratio depends on initial pressure of HBL, permeability and porosity.
- Desirable production target can be identified and be directed in the exploitation.

Potential of gas production from hydrate deposits depends on occurrence features of the hydrate deposits and production methods, and fundamentally it is determined by geologic conditions of the hydrate reservoir. The geologic conditions mainly include reservoir porosity (Φ), hydrate saturation (SH), formation permeability (K), thickness of hydrate-bearing layer (HBL) (H), initial pressure (P0) and temperature (T0) of the HBL. Profound differences of the conditions have been revealed by the global marine drilling programs. Orthogonal design, as a statistic method, is employed in this work to systematically investigate the relative importance of these diverse geologic conditions on hydrate decomposition as well as production performance of gas and water from the Class 2 offshore hydrate accumulations. The analysis results show that the order of the significance levels of the geologic conditions on cumulative gas production is K > Φ> SH > T0> P0> H; while the order of that on the water-to-gas ratio is P0 > K > Φ > SH > H > T0. The results suggest that it is favorable for production from the hydrate deposits characterized by the conditions of the high permeability, moderate porosity (40%), moderate-to-high hydrate saturation (38%-67%) and the low initial pressure (10.79-13.38 MPa). This research gives a forward sight for production prediction and provides a reference in selection of production target.